Packaging materials such as hollow containers, trays, lid materials, inner layer materials of paper containers and inner coating materials of cans are brought into direct contact with foods or drinks such as juice and water. Therefore, the packaging materials are required to be excellent in gas barrier properties, odor-keeping properties, etc. As the packaging materials, polyethylene terephthalates have been paid much attention.
The inner layer materials of paper containers require high heat-sealing properties, high ductile properties and high impact resistance, and the inner coating materials of cans require high ductile properties, high impact resistance and high adhesion to the can materials. However, conventionally known polyethylene terephthalates are not always sufficient in those properties. For example, a polyethylene terephthalate homopolymer derived from terephthalic acid and ethylene glycol is insufficient in heat-sealing properties and impact resistance, and a crystalline polyethylene terephthalate copolymer composed of terephthalic acid and ethylene glycol and a small amount of a copolymerizable component other than ethylene glycol is not always excellent in the ductile properties and impact resistance. Further, an amorphous polyethylene terephthalate copolymer prepared using cyclohexanedimethanol in an amount of about 30% by mol as a diol component (commercially available under the trade name of PETG) is relatively high in the ductile properties and the impact resistance, but the level of the impact resistance is not satisfactory, and the odor-keeping properties thereof are insufficient. Moreover, the heat resistance of the amorphous polyethylene terephthalate copolymer is poor, so that a problem resides when conducting a retort treatment or a hot charging using a product of the copolymer.
The present inventors have studied to solve the above-mentioned problems in the prior art and to obtain packaging materials excellent in odor-keeping properties and also showing sufficient ductile properties and high impact resistance. As a result, they have found that a polyester composition comprising a polyethylene terephthalate copolymer having a specific composition and specific physical properties and a specific ethylene copolymer ionomer is excellent in the above-mentioned various properties, and accomplished the invention.